Electric discharge apparatus for alternating current motors



1953 w. E. LARGE ETAL 34 ELECTRIC DISCHARGE APPARATUS FOR ALTERNATING CURRENT MOTORS Filed Sept. 27, 1952 6 Sheets-Sheet l TKS SK F04 -oo--o ZTK ITKZ Electronic Power Unit.

WITNESSES: INVENTORS 5 F|g.|A. William E. Large and Robert F. Barre l. 7% BY Q WWM ATTORNEY Dec. 22, 1953 w. E. LARGE ETAL 2,663,834

ELECTRIC DISCHARGE APPARATUS FOR ALTERNATING CURRENT MOTORS Filed Sept. 27, 1952 6 Sheets-Sheet 2 WITNESSES: F g B lNg/ENTORs William .Lorge m 2141 and Robert F. Burrell. BY fi '7 M ATTORNEY Dec. 22, 1953 w. E. LARGE ETAL 2,663,834

ELECTRIC DISCHARGE APPARATUS FOR ALTERNATING CURRENT MOTORS 6 Sheets-Sheet 5 Filed Sept. 27, 1952 Eta-E 1 i I INVENTORS William E. Large and Robert F. Barrell.

ATTORNEY OIIZ"" '09 caloe1 I I I m l E I I I I I I" I WITNESSES:

Dec. 22, 1953 w. E. LARGE ETAL ELECTRIC DISCHARGE APPARATUS FOR ALTERNATING CURRENT MOTORS 6 Sheets-Sheet 4 Filed Sept. 27, 1952 rell.

INVENTORS William E. Large ond $obert F. Bar

WITNESSES:

ATTORNEY Dec. 22, 1953 w. E. LARGE ETAL ELECTRIC DISCHARGE APPARATUS FOR ALTERNATING CURRENT MOTORS 6 Sheets-Sheet Filed Sept. 27, 1952 uouam .632

Pbwer factor in X,

Power factor Angle Fi g.' 3.

Poiemiol of one w m a m 1 O 6 m 4 e 2 s O h D.

O o. 8 6 uoo:o

Time

Phase Delay INVENTORS William E. Large ond F Qobert F. Borrell.

WITNESSES:

ATTORNEY Patented Dec. 22 1951;

ELECTRIC DISCHARGE APPARATUS FOR ALTERNATING CURRENT MOTORS William E. Large and Robert F. Barrell, Lancaster, N. Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 27, 1952, Serial No. 311,912

14 Claims.

Our invention relates to electric discharge apparatus, and has particular relation to apparatus for controlling a heavy duty polyphase motor. This application is a continuation-in-part of our application, Serial No. 122,694, filed October 21, 1949, and assigned to Westinghouse Electric Corporation.

The above-mentioned parent application discloses several embodiments of a motor drive including a heavy-duty polyphase motor such as that used in driving an automobile body press and electronic means for controlling the motor. The phase windings of the motor are, in each case, connected through anti-parallel electric discharge devices to the phase buses of a commercial supply and the discharge devices are controlled to attain the desired motor operation. Our present invention is the result of an extensive investigation conducted on the 'drive disclosed in the parent application.

A heavy duty motor such as is involved in our invention at a given voltage draws a high current in the locked rotor condition, that is, when it is starting. Such a motor when starting then imposes a heavy drain on its supply and where the supply is of limited capacity, as is the situation in many large cities both in the United States and abroad, the starting of the motor produces a large decrease in the potential of the supply which is objectionable to those deriving power from the supply. For example, the starting of a heavy duty motor in a shop in a complex industrial area such as mid-town Manhattan may cause fluorescent lights in a drafting room which are connected to the same limited supply as the motor to flicker.

Heavy duty motors which run continuously and are started only at relatively long intervals do not in the respect just discussed present a serious problem as motors, such as those driving automobile body presses, for example, which run intermittently. The latter must be started repeatedly at relatively short intervals and at each start they affect other apparatus on the supply. The intermittent motors and motors on related apparatus must also frequently be inched or jogged when the tool which they drive is being set up. Starting current is applied repeatedly to a motor operated in inch and the supply fluctuates correspondingly. Intermittently operated motors of large rating and motors of large rating frequently operated in inch controlled in accordance with the teaching of the prior art present so serious a problem to limited supplies that the utilities frequently bar or limit this use.

It is often also desirable to accelerate a heavy duty motor at a predetermined rate. Such accel! eration is not readily achieved with the apparatus available in accordance with the teachings of the prior art.

It is accordingly an object of our invention to provide apparatus for driving a heavy-duty motor which shall operate without producing obj ectionable fluctuations in the supply when the motor is starting.

Another obj eot of our invention is to provide apparatus for driving a heavy-duty motor, which shall readily permit such a motor to be operated at the will of an operator, continuously, intermittently or in inch without producing objectionable fluctuations in the supply.

A further object of our invention is to provide apparatus for driving a heavy-duty motor which shall permit the driving of very large motors from power supplies of capacity insuftlcient or just sufficient to meet the starting current demands of the motors.

It is still another object of our invention to provide apparatus for driving a heavy-duty motor which shall include facilities for accelerating the motor at any desired rate over a reasonable range.

We have found that a heavy-duty motor drains far less current at a given voltage when running at its usual speed than during starting and we avail ourselves of this property of the motor in our invention. In accordance with our invention we provide motor drive apparatus which when the motor is operating in or near the locked rotor condition, automatically maintains the voltage on the motor at a substantially lower magnitude than the voltage of the supply, and as the motor speed increases automatically raises the motor voltage to the running magnitude. This object is accomplished by means of electric discharge devices which are interposed between the power supply and the motor and are so controlled by phase shift circuits as to supply the motor at the appropriate voltages. The phase shift circuits determine the instants in the half periods of the supply during which the discharge devices are to conduct when the discharge devices are fired. These discharge devices are usually ignitrons but they may be devices of other types. Hereinafter they are referred to as electric discharge paths. The word path is intended to include within its scope discharge devices having a plurality of main discharge paths in one envelope.

A contributing factor to our invention is the realization that the settings of the phase shift circuits need not cover a wide range or phase angle. This arises from the fact, as We have found, that the power factor of a heavy-duty 3 motor decreases substantially as it passes from the locked rotor to its normalspeed running condition. In accordance with a specific aspect of our inventionj-then; the phaseshiitcircuits may be setgonc'e andior all, to fire the'discharge devices at instants corresponding to the running Power factor.

tently or in inch or in jog presents noserious starting voltage be even smallerthanthc Vol agecorresponding toth'at produced by firing the discharge'devices at instants corresponding to the running'power factors" In accordance with afurther-aspect-of our'invention",'we provide a control circuit for each of the discharge devices which includes means effective during starting for preventing each discharge device from being rendered conductive until-an instant substantially 'later in the half periods thanthat correspondingto therunning power factor' of the motor. This preventing means "is rendered in'ei ie'ctive when the motor comes'up to normal speed and-the discharge device isthen fired to correspond-to the running-powerfactor of the motor. Thecontrol circuit may also include preventing meanshaving a number of'setting's such that for each setting, the discharge'device is rendered conductiveat a difierent insta'nt" in any half period. We further provide in accordance with ourinvention means for chan ing'these'settings as the-motor comes up to'speed'so that as the motor comes up to speed the discharge devices are-rendered'conductive at'earlier instants in the half periodsof the'supply and at i'ull speed-full power-is supplied to the motor. The change in the settings may be-effected-in response to the speed-of the motor, or from-a timing mechanism which changes-the set-tings'at predetermined instants ccrresponding to the "difierent-speeds of the motor. The former embodiment'of our invention isused in-situations in which the variation-in speed :01": the motor is not entirelypredictable as where the motor is -started-xunder load-. The -latter embodiment of "our invention is --used in situations in which" the variation of the speed of themotor is predictable. Such a situation arises in rnotors which reach fulls eed beforethe load is'applied to them, thatis, before they execute the power stroke.

In apparatus in accordance with our inven tion whichincorporates the iacilities'for chang' ing the delay inthe firing as the motor comes up to speed the range of the changeis relatively smalhofthe order'of a quarter of a periodbf thesupply. This condition arises because "one limit: of therange is the running power factor angle by themotor which itself of the order The novel features that we consider character istic of our invention are setforth "above; Our invention itself, however, both as to its organizationa'nd itsrnethod of operation together with additional objects and advantages thereof, will I beunderstood from "the following description When a motor in a drive which is so set is started, it operates at reduced voltage because it's starting power factor is "higher than iof specific embodiments when read in connection with the accompanying drawings, in which:

Figures 1A through 1D together constitute a circuit diagrainiof a preferred embodiment of our invention; v

Figs. 2 and 3 are graphs showing the characteristics of the motor of Figs. 1A through 1D;

Fig. 4. is another graph showing the operation or" the power unit of Figs. 1A through 1D;

Fig. 5 is a diagram illustrating a modification of our invention.-

Description Fig. 1

The apparatus shown in Figs. 1A through 1D includes a polyphaseheavy-duty motor M, an electronic power unit and a starting unit. The motor M and the power unit are supplied from the buses Ll, L2 and L3 of a commercial threephase supply. The starting unit is supplied from auxiliary buses AL! and ALE which are energized from a transformer IT.

The motor M may be of the induction or synchronous type and it includes a plurality of phase windings W i, W2 and W3. In the motor shown in Figs. 1A through 113, these phase wind ings are connected in Y. The windings may also be connected in delta, either directly or in the manner illustratedin Fig. 3 of our above-mentioned parent application.

The electronic power unit includes a plurality of pairs of ignitrons I-l, I-Z; I-3,- L4; and I-5, I-B. Each ignitron has an anode 1, a cathode 9, an igniter i! and an auxiliary anode E3. The ignitrons Li and L2 are adapted to be connected in antiparallel between the bus LI and the winding Wl through a contact FKI of the contactor KF (see 11)). which is actuated when the motor M is to rotate in a forward direction or between the bus L and thelwinding W i through the contact RKZ of a contactor KR which is actuated when the motor M is to rotate in the reverse direction. The ignitrons I-3 and Liam similarly adapted to be connected between the bus L2, through contact FKZ, or bus Ll, through contact 3K3, to winding W2. I-t are directly connected between bus L3 and winding W3. is controlled by the conduction of the ignitrons, and may be low or high depending on the instant in the half periods of the supply at which the ignitrons are fired.

Each ignitron I-! through L6 is providedwith a firing circuit FCl through FCd. These firing circuits are alike for all ignitrons and only and F05, is shown in detail. The firing. potential is derived from a capacitor C which, we may calla firing capacitor which, is connectedto the cathode 9 ofthe corresponding ignitronI-E through a resistor. i5 and to the ,igniter,li through a thyratron FT which we may call a firing thyratron and a peak-liniitingreactorl7. The thyratron FT has an anode l9, a cathode 2i; and a control electrode I 23. nected through thereactor ll to theanode i9 and the cathode 23 is connected to .theisniter I l.

2T. In the case ofiiringthyratron FT for igni tron I-E one of these buses is L3, the other bus is Ll or L2 depending on Whether the forward contactor KB or the reverse contactor KRis actuated. The primary 2P of the transforme'rf'ZT Y is adapted to be connected to the buses through normally open contacts SKEi'of a relay RS which Ignitrons I-5 and The voltage applied to motor 1V3 The capacitor C. is con:

we shall call the starting relay. This relay is controlled from the starting unit and has a plurality of normally open contacts SKI through one each for each firing circuit FCI through FCt respectively. One of these contacts is connected in the supply to the primary 2P of a charging circuit for each of the ignitrons.

The firing of an ignitron is effected by discharging the capacitor C through the thyratron FT. The are is first picked up by the auxiliary anode l3 and transferred from it to the main anode l. The auxiliary anode is supplied through a transformer 3T from the same buses as the corresponding firing capacitor C. The secondary 38 or" this transformer is connected between the auxiliary anode l3 and the cathode 9 through a variable resistor 3i and a rectifier 33 and the auxiliary anode and cathode are shunted by a fixed resistor 35.

The transformer 2T of each charging circuit and the transformer 3T are so connected to the corresponding supply buses that the corresponding firing capacitor C is charged during the half periods during which the auxiliary-anode-cathode potential of the corresponding ignitron is negative. The capacitor C for each ignitron is thus ready to be discharged when the auxiliary-anodecathode potential of the corresponding ignitron is positive. The main-anode-cathode potential of each ignitron depends on the main-anodecathode potential of other ignitrons since the main-ahode-cathode paths of certain ignitrons are in series. But the polarities of the mainanode-cathode potentials are such that each ignitron may in its turn conduct during an interval when its auxiliary-anode-cathode potential is positive.

Between the control electrode 23 and the oathode 2! of each firing thyratron FT, a composite potential is impressed. This potential is derived from a pair of conductors AL3 and AL4 through transformers QT and 5T and consists of an alternating potential derived from transformer 4T and impressed across a capacitor 27 and a potential derived from transformer 5T through a rectifier 29. The rectifier output is unfiltered and the rectifier it is so connected as to impress inverted rectified pulses in the control circuit. This inverted rectified potential has a wave form consisting of a succession of loops interposed between cusps which occur at the instant of zero potential of the alternating potential derived from transformer ET. The cusps provide potentials of short duration for renderin conductive the firing thyratrons FT when the alternating potential is of proper magnitude.

The conductors ALB and AL4 which supply the control potential to the firing thyratron FT are themselves supplied from a transformer ET, the

primary EP of which is connected across two of the buses L! or L2 and L3 depending on the condition of the contactors KF and KR. The secondary of this transformer has a pair of terminal taps and an intermediate tap. To one terminal tap a capacitor CP which may be called a phase shift capacitor is connected; to the other terminal tap, a variable resistor RP is connected in series with a pair of fixed resistors RP! and R1 2. The resistors RP, RP! and RPZ may be called phase shift resistors. The conductors ALB and ALi, which supply the primaries 41? and SF of the transformers AT and ST, are connected between the junction of the capacitor CP and the fixed resistor RP2 and the intermediate tap of the secondary 55.

The fixed resistors RPI and RP2 may be shunted out, by contacts IIK5 and'2TK5 of a pair of relays IRT and ZRT respectively. These relays are connected to be energized from a tachometer generator G driven by the motor M. Under certain circumstances, one or both of the resistors may also be shunted out by a manual switch SM.

We shall call the circuit including capacitor CP and resistors RP, RP! and RP2 a phase shift circuit and label it PH. The potential impressed by the circuit PH across the primaries of the transformers 4T and ST is displaced in phase with reference to the potential of the buses Ll or L2 and L3 from which the transformer GT is energized by a phase angle which is dependent on the magnitude of the capacitor CP, the setting of the. variable resistor RP, and the magnitudes of the fixed resistors RPI and RP2. This phase shifted potential is impressed through the transformers 4T and ST in the control circuit of the firing thyratron FT. The composite potential impressed in the control circuit of the firing thyratron is then composed of an ordinary sinusoidal potential having a phase relationship to the potential from the buses as determined by the phase shift circuit PH and a potential of cusp wave form, the cusps of which coincide with the points at which the sinusoidal potential passes through zero. This composite potential has amagnitude sufiicient to render conductive the firing thyratron F1 during a short time interval (coinciding with alternate cusps) of each period of the supply. The phase of the potential derived from transformer ST and the setting of the capacitor C1? and the resistors RP, RP! and RPZ are such that this short interval occurs during the half periods following those in which the firing capacitor is charged. The instants when the firing thyratron FT is rendered conductive also occur while the potential from the supply which is impressed between the auxiliary anode l3 and the cathode 9 of the associated ignitron (1-5) is positive. Firing potential is thus impressed on each ignitron at a certain instant in its positive half period of auxiliary-anode potential as determined by the setting of the resistors in the phase shift circuit PH. The ignitrons I-l through 1-6 are so connected that the main anode potential of each is positive during a large proportion of the interval during which the auxiliary-anode potential is positive.

The firing circuit for only one ignitron, 1-5, is shown. The firing circuits for the others are identical. In each case the firing potential is derived from a capacitor C which is charged from a transformer 2T, the primary circuit of which is closed by a contact SKI, 2, 3, 4 or 6 of the starting relays RS when the motor M is to be rotated. In each case a thyratron FI controlled from a phase shift circuit is provided for discharging the capacitor C at a predetermined instant and this circuit includes a plurality of fixed resistors RP! and RP2 adapted to be shunted out by contacts ITKI, 2, 3, 4 or 6 and ZTKI, 2, 3, 4 or 6 of relays IRT and ZRT actuable from a tachometer generator G. In each case, the arc may be picked up by the auxiliary anode l3 which is positive when the firing current flows.

The phase shift circuit PH which supplies the control circuit of the thyratron FT in each firing circuit FCI through FCB constitutes an important feature of our invention. The importance of thisfeature will now be explained,v with ref.-

aromas-4 ierencertor'liigs; wig. 12' presents-stale graphs, 1(a) :and 01h) hich :s'how 112118 :speerb power- 1 actor :characteristics ;of reactor graph ra) ithei'motorspeedeiszshowmasea: function:of 'thevpowerifactor;11in Egraph .Lb) it :is shown as a function: ofitheiipowerefactoriangle, that is, of the angle of lag of the motor current withreference to'the potential impressedthereon. These graphs ar-e -plotted for: a typicali heavyduty motor Les-can he seen, the power fa'ctorzo'f :the: motor varies 'fromapproximate1y- 40i% at zero speed: to- 17 at a running speed indicatedbyt across 1011 graph "(11). 'Bhe correspon'ding power -iactor a-ngle varies -frcm a lasg of=366 :to =a-;la'g of 80.2at running speed as-shown on -rgraph tb).

Zn 1 ig3 voltage'isplotted vertically-andstime horizontally. in: this graph; the isine waveerep resents the :voltage of: :one :phase: of ithe-i source L -L2 B3. The: shaded areas"- betweenvthetphase angles 60 and: err nand 246" and 1260 ;:cepr.e sents the range of -variation'of therzpower-factor angle 'as the =-motor speed varies zfrorn: zero; to the running speed. 3A5: cani-ber. seenpthis range extendsoverfiapproximately 14,ifrom: approximately -66=aat zero 'speed-i'tofiilfl" at fullspeed.

Figure: 3 shows that i thei speed- -power factor characteristic- 0f the -m0tor? Mvma'kes, available a' facility tor startingthe motor ataaiionrenvoltage than"the volta'ge at which it loperates. The motorM may be started at a phase angle corresponding -to :"its a running power factorz" angle, thatrispat aphase angle oi 80%. Since the starting power-factor angle:of the :motorBisJGGP; the

:motorso startd is 'supplied tat a::reduced:.:voltage. As themotor:comes upltmspeed, its powerfactor ang1e approaches thexstartingsangle-iand full power is- 'supplied tm it. "JIEhe :starting as jus't explainediiis effectedlby ffiring Fill-1e? ignitrons 1 through "BB -through: which-:the motor iis supplied at the appropriate tangle in their. lpositive half periods, which-timthecase "illustrated, would-he at an angle-of 80 followin'g the' instant :ofizero potential.

I'm-accordance iwithfonesaspect of our inven- 'tion; theithyratrons are set to; supply? the motor art rt. t a starting 1 angle correspondin'g to: itsrun- 'nin'g powerdactorl angle. This ob'je'ct :is accomipli'shed bywsetting Othe: -.pha'se-:shifting=.-:circuit :at :the proper-setting. slnrsituationsiwhere.Lthe re- -duction .am= tvoltages attained in ;.this.:.manner;:is adequate, only the variable resistorsfiPianddche capacitor :CP lneedzahe connected :inpea'chcphase shifticircuitil?l-I.v Under suchacircumstanceg. the

twoiixedresistorg-RP lzsandERPlmayhefshunted l out by::the manual: switch-SM.

Inrothertsituations; the voltage zavailable by setting at. the lrunningipowerefactor angle is. not :isufficiently low for 'starting. Undersuch" circumstances, .a plurality ofvresistors such as athevtwo fixed. resistors RBI and RP2- :in the phase ishift circuit may be -added. 'l'These resistors:are-o'f such inagnitude as' to delay the =starting by' an angle substantially greater than the runningpower factor angle. The *delay' is'sufiicient -to enablethemotor'M tobe started or to be inched without *materially affecting the out-put voltage oithesupply. *When the motor M is tobe inched, *the "fixed resistors "RP l-= and EFT-remain in'" the circuit during the inching and the motor is operatedi in "inch-at reduced *--voltage. *When the motor 'M-is to operate continuously, facilities are "prciviiied for:shuntingmut the resistors as the 'lmotoricomesupto speed. Su'ch facilitiesare t-he :the :tachometer generator AG and progressively shunt out the, fiXed-resistorsso that eventually the motor it/Loperates, atiullrspeediwith full power suppliedthereto.

.Withzthese :resistors RP! andBBZ :::in ,the circuitgthevariable-resistor .RF -;is :set :so that when the resistorslRP l:..and RPZrareshunted out the phase shift circuit PH causes the ignitrons .tO'ICOIldIlCt .at :thea full speed-'powereiactor' angle in i the half periods of the potential impressed. .Thus the shift in ttheangle .ofyfiring eefiectedstby shunting-outiithe"fixed resistors RPl and R122 is relatively xsmall,.;of athe order :of 1 /3 or /4-of a period.

The-starting :unitcontrolsthe operation of the :motorM. This unit-includes axselector switch SS which selects the :mode ofzoperation. of' the motor M- and has. contacts S'i/S2, S3, St, S5, St, S! and S3. One of three modes maybe -selected, depending on the setting of the switch SS. Themotor M may be operated-only'for a single cycle; it may be operated. continuously; or it may be inched.

The single cycle operation is controlled 'bya limit switch'LS having-sixcontacts L-i through 195. The limit switch LS is actuated by'the motor as -it-rotates,-through gears (not shown) and stops the rotation-at theend-of a cycle. During continuous operation, the contacts L 3 through L-% are shuntedbycontactssti, St, S1, S3 of'the selector switchSS. If desired, the swi'tcn'LS niaybe'driven through reductiongears so that motorM executes a number of complete revolutions during single-cycle: operation.

The selector switch SS is set --to. start 1 whatever "operation of -n1otor 'M- is desired. To start; the motor in single-cycle or continuous operation once the selectorswitchiSS isset, a run button BR isprovided. This; button has-a normally -closedcontact'fifl anol'a'normally open, contact 32.

'Whenitheselector switch SS..;in set forinch, ,the forward inchingioperationo is controlled by forward .inchybutton BF and the reverse inch operated by a. corresponding button BV. ,Each .OfthGSGbllttOl'lS'lBF and BVhas a normally open contacted and- 36 respectively andanormally closed contact 37 andi'tt respectively, anormally open contact3and '3t ofone buttonheing connectedjin series with a normally closed contact .of theotherf38'orj3lso that the buttonsare inter- ;locked andactua'tion-loflone renders theother ineffective.

The starting unit also. includes .the forward .oontactor KF an'dwthe reverse ,contactor These contactors, are adapted to '.be, energized from rectifiers'fiil andfiifi respectively whichare supplied from. the buses ALI and In addition-to thev contactsFKl and FKZjthe forward .conta.ctor includes. a. contact FK3 in theenergizling circuit ofthe. rectifier. it. This contact EK3 lis openiwhen contactor' KF is energized and .preczentsnontactor KR fromlbeing energized. Con- .tactor KR..lincludes a ,similar. normally Closed contact 7 R5123 .in. the; energizing circuit for vthe rectifier-t 38. l

. The, starting unitfurther.includes. a main, con- ..trol relay R0. .The main control relay .RChas fourv normally opened contacts-4 l 43, .45 and 41 and onenormally closed contact-4S. Two of the normally opened contacted-5 and l? are connected Ana. circuitwith .theexcitingucoil, of the forward icontactor'KP and the-rectifierfiQ and .whenthe delay RCH is energized, energy, is supplied tothe coil of contactor KF from the-rectifi,e1:: .3.9. V The relays: l'R nsand ifi'liitwhich mecenergize'd from iQQIItaQtOILYKF I .rth :een r ized closing; the: im-

ward contacts FKI and FK2 in series with the ignitrons I-I and 1-2 and 1-3 and 1-4. The other contacts 4!, 43 and 49 of the relay RC are connected in circuits so as to advance the sequence of operations carried out in starting the motor.

There are also a pair of auxiliary relays RAI, RAZ. The relay RAi has two normally open and two normally closed contacts 51, 53 and 55 and respectively. The normally open contacts 5| and 53 are connected in a circuit with the coil of an auxiliary relay RA2 and this relay is energized when the auxiliary relay RAI is energized. The contacts 55 and 5'! are connected to advance the starting operation. The relay RA2 has four normally open contacts 58, BI, 53 and 65. Two of these contacts, 59 and BI are connected to lock relay BM in the energized condition; the other two to advance the sequence of the starting operation.

Still another relay RR is provided. This relay is actuated by the run button BR, and it is connected to be energized through a pair of the normally open contacts 53 and 55 of the auxiliary relay RA2. The relay RR has four normally open contacts 51, 59, H and 73. Through two of these contacts ii and I3 another relay RM which we may call the motor releasing relay is energized. The other contacts 61 and B9 are connected to control the running of the motor.

The relay RM has six normally open contacts 75, ii, i9, 8!, 5i and i 19. Through two of these contacts Ti and "iii the brake solenoid SE is energizetl, to release the brake for the motor M, and the timer relay RT i energized. Through the other contacts 55 and SI, the relay RM is locked in energized condition; The timer relay RT has two normally open contacts 83 and 55. Through one the starting relay R5 is energized; the other functions during the inching operation.

The starting unit also includes a further relay RV which is actuated during the inching in reverse. This rela includes four normally open contacts Si, 39, iii and 53. At two of these (9| and 33) the energizing circuit through the exciting coil of the reversing contactor KR is closed through the rectifier do. The other two, Bl and 85, advance the starting operation.

StandbySingZc cycle For single cycle operation, the selector switch SS is set with contacts S3 and S4 closed, and contacts Si, S5, 538, Si and S8 open. With the contacts S5, S5, Si and S8 open, the limit switch LS is eiiective. With the motor M at rest, this limit switch is in a position in which contacts L-i and L-2 are closed and contacts L-S, L-Ll, 1-5 and. L-G are open. 7

With the selector switch SS and the limit switch LS set as described, a circuit is closed through the coil of the main control relay RC. This circuit extends from the bus ALI through a conductor ti, a stop button BZ, contact S3, a conductor 58, aconduotor on, the coil of relay RC, a conductor i553, contact or to bus ALE. Relay RC is, therefore, energized. Another circuit extends through the coil of auxiliary relay RAE from bus Aiii through the conductor 9'5, the stop button 32, contact the conductor 95, the conductor ioi, the normally closed contact 38 of the run button the coil of relay RAi, the conductor contact S5 to the bus AL2. I Relays RC RA then pick up. At the two now closed contacts 25 and. A? of relay RQ the forward contactor KF is energized, closing its normally open contacts FKI and FKZ in the electronic power unit and conditioning the unit to energize motor M. The contactor KF also opens its normally closed Contact FK3 in the energizing circuit for the reversing contactor KR, thus preventing the operation of the latter. At this point, then, the auxiliary anodes I3 of the ignitrons 1-! through L6 are supplied with potential and through the transformers ST and the transformers 2T are conditioned to supply charging potential to the capacitor C.

Through the now closed contacts 5| and 53, of the auxiliary relay RAI, current is applied through the exciting coil, of the auxiliary relay RAE and the latter is energized. This current is supplied in a circuit extending from the auxiliary bus ALI through the conductor 9'1, the stop button BZ, contact $3, the conductor 99, contact L-i, a conductor I85, the now closed contact SI of the auxiliary relay RAI, the exciting coil of the auxiliary relay RA2, the now closed contact 53, a conductor I91, the contact L4, a conductor I59, the contact S4 to the bus ALZ. The relay RAZ then picks up.

The starting unit is now conditioned for single cycle operation.

OperationSingZe cycle After the starting unit is set for single cycle operation, the motor M is started by actuating the run button BR, thus opening its normally closed contact 31'? and closing its normally open contact 32. By the opening of the normally closed contact an, the auxiliary relay RAI is deenergized and drops out. But the other auxiliary relay RAZ remains locked in energized position through a pair of its now closed contacts 59 and 5! and through the contacts L-I and L2.

t the closed contact 32 of the run button BR, a circuit is closed through the exciting coil of the relay RR. This circuit extends from the auxiliary bus ALI through the conductor 91, the stop button BZ, the contact $3, the conductor 99, the conductor IDI, the now closed contact 32 of the run button, the now reclosed contact of the auxiliary relay RAI, the now closed contact 63 of the auxiliary relay RAZ, the exciting coil of the relay RR, another now closed contact 65 of the auxiliary relay RAZ, a now reclosed contact 5'I of the auxiliary relay RAI, contact S4 to auxiliary bus ALZ. Relay RR now picks up. At its now closed contacts H and I3, this relay closes a circuit through the exciting coil of the motor release relay RM. This circuit extends from the auxiliary bus ALI through the conductor 91, the stop button BZ, contact $3, the conductors 99 and it'll, the now closed contact 32 or" the run button BR, the now closed contact 55 of the auxiliary relay RAI, a now closed contact II of the relay RR, the conductor III, the now closed contact 4! of the relay RC, a conductor II 3, the exciting coil of the relay RM, a conductor II5, the now closed contact 13 of the relay RR, the now reclosed contact 57 of the relay RAI, the conductor I33, the contact S4 to the bus AL2. The relay RM is now energized and at its now closed contacts l5 and TI closes a circuit through the brake solenoid SB, and also a parallel circuit through the coil of the timer relay RT. These circuits extend from the auxiliary bus ALI through a now closed contact 71 of the relay RM, a conductor I II, the brake solenoid SB, and the winding of the timer relay RT, a conductor HS, a now closed contact I9 of the relay RM, a conductor [2| to the bus ALZ. The brake B is now released and the timer relay RT times out.

The timer relay RT is setter-time; out in ap proximately two seconds; motor brake B is. entirely. released. When the timer relay. timesout, ittclosesone'of its normally open contacts 83, closing a circuit through theexciting coil of. the starting relay RS; This circuit extends from the auxiliary bus ALE through the now closed contact ll of the relay RM, a conductor II'I, anow closed contact 51 of the relay RR, a conductor. I23, a conductor I25, the now closed contact 83 of the. timer relay RT, a conductor I21, the-exciting coil of the starter relay RS, a conductor I29, a conductor I3I, another nowclosed contact 69 of the. relay RR, a conductor I33, another now closedcontact i9 ofthe relay RM, the conductor I2I tothe auxiliary bus AL2.

The relay BS. is. nowenergized closing its contacts SKI through SKIS in series with the primaries 2]? of the transformers. 2T which charge the firing capacitors C. Thecapacitors are then charged during the half periods during which the auxiliary-anode-cathode poten-- tial on the associated ignitronsI-I through 1-5 are negative. During the half periods during which the auxiliary-anode-cathode potential are positive, the'firi'ngthyratrons are rendered conductive at instants predetermined by the setting of the variable resistor RP and the magnitudes of the fixed resistors RPI and RPZ. These instants are late:in the halt period for each ignitron andas each. of the ignitrons. is in its turn rendered conductive, current is supplied at reduced potential to. thewindings WI, W2, W3 of the motor M The manner in. which the. ignitrons 1-! through I-E- fire may be understood. with. the help of Figure 4. Inthis vie v,.voltage is plotted vertically and time,. horizontally. The interlaced sine curves representthe voltageof each of the buses LI, L2 and L3 relative. to an. artificial neutral, for example,.thev junction. of the windings WI, W2, W3. of .the motor M- Each of the sine curves then'representsithe voltage impressed between the corresponding supply. bus

(LI, L2, or L3) and thisjunction. Thevoltage impressed across theignitrons I-I: through 1-6. when the latterare. non-conductive is made. up of combinations of thevoltagesrepresented by the sine. curves. Thus when the. ignitrons; arev non-conductive. theanode I oflL-I is atthe potential of bus LI and. the cathode. {lei-1. 5 at the potential. ofI bus L3. Similarly the anode I and cathode. 9 of ignitrons I-.-3 and I'i-2- respectively are atthe potentials of buses L2 and LI respectively and'the anode I andcathode 9 of 'ignitrons 1-5 and L l-respectively are at the potentials of buses L3. and- L2" respectively. These potential differences are. of interest because at any instant when motor M is being energized current flows in. series through the ignitrons 1-! through L5,, and the potentials described are. the potentials. under which the current flows. The auxiliary-anode. circuits are energized lndividually and. not in series. Thus,.since contactor KF is energized, potential. between the auxiliary anodes I3:and the. cathodessof ignitrons I -5.and 1-5.. is derived. for. eachignitron directly from thebuses LI. andMLS; that for ignitrons. 1-.3. and 1-4,. from. the buses. L2. and L3; and thatzfor. ignitrons. I-.-I1 andI-Z; from the buses LI and L2.

It may be assumed-that the contacts SKI of .th ,.-starting-1 relay RS close at -ancinstant- At this. time,- the.

represented byL the; vertical v line. on: they left of Fig, 5.-. Itmay also. be; assumed. that. thefiring circuitsEGlthroughaifilciir foreach of the isniters are. set:- to. supply igniter current atan angle, represented by thesma-ll. crosses. onthe corresponding curves. Under such circumstances,- the firing: capacitor C. oil the firing circuit. FCd is. charged: during; the. positive half period representedby the. positive loop on the extreme left.- Igniter. current then first flows throughthe igniter: H ofignitron. 14. While igniter current isefiowing, secondary 38. of firing circuit- RG4 impressesa positive potential betweemthe auxiliary-anode IBandcathode a of.

' ignitron-117 i.- and an. auxiliary arcis produced.

Current then. fiows from one terminal of the associated secondary-.33 through the variable resistor '3 I the rectifier. 3'3, zthen auxiliary anode I3 and. the cathode 9 of ignitron 1-4 to theother terminal of the.secondary;3S.- The ignitronI-4 is-then in:.a-condition:-to conduct ii" the proper potential. is suppliedtothe anode. But this potential is-not: at. the'moment. supplied since none of the other ignitronsJ-I toI-3; 1-5. and I6 are-conductive, .and for. the. moment current continues to flowthroughthe above-traced circuit;

In the-meantime; the. capacitor C of firing circuit. FCI has charged. during the interval represented by the negati-ve loop ontheleft of Fig. 4. .Igniter current is then-supplied to the ignitron I-l atitheinstantcorresponding to the cross on the succeeding.. positive loop, and arc isproduced at the. auxiliary anode I3 of the: latter. Current may. now flow through ignitrons I-Iand 1-4 andisince both ignitrons are in condition to. conduct,. current flows irom bus- Li through contact FKLignitrcn I-i, phase windings WI andWZ offmotor M, ignitron 1-5, contactFKZ-to busLZ. Itisiseen that the direction of the current. is from. the phase terminalof. WindingWI towards the neutral and from theneutral' to the phase terminal of wind ing W2.v

While. current is thusflowing through windings WI. and W2, ignitron Ieliis supplied with firing current at an. instant corresponding to the cross on its curve, andis rendered conductive of a periodafter ignitron I-i). Current now begins-to buildupv in.a circuit including winding W3. This-circuit extends from bus Li throughcontact FK-I, ignitronI-I, windings Wi and-W2; ignitron 1-6 to bus L3. Current is now flowing'from the phase terminal. of W! to the neutraland from the. neutral to the phase terminalsWZ and W3; The current inwinding'Wfi is building up andin W2 is decaying and eventually the current'through the latter. drops to zero;

One-sixth. of. a period after. ignitron 1-6 was rendered conductive igniter. current is supplied to theignitronI-ii. Ifignitron I4 is still conductive, current at this timeffiows through the auxiliary-anode, circuit;of'ignitron1L-3, and ignitron I-3becomes conductive. after ignitron I- l has becomenon-conductiva- I'f'ignitron 1-8 is non conductivewhen the ignite-r current is plied. toignitron I- -3. ignitron L3; becomes conductive atonce. Ineither. event, current builds up in a circuitextending from. bus LI, through contact. EKZ,.,ignitron.I-3;.phase windings W2 and W3 and ignitronL-itosbus. L3.

The. current...in winding, W2. in a direction fromritsterminal to the. neutrall'is. now building unandithe current .inwindi'ngWI fiomtheterminal to the neutral is decaying. The next ignition to conduct is 1-2. It conducts after ignitron I-I becomes non-conductive and current flow in a circuit extending from bus L2 through contact FKZ, ignitron 1-3, winding W2, winding WI, ignitron 1-2, contact FKI to bus LI. Current now builds up in winding WI in a direction from the neutral to its terminal and current in winding W3 decays.

Ignitron 1-5 is the next to conduct, and it conducts after ignitron I-S becomes non-conductive. Current then flows from bus L3 through ignitron I-5, windings W 3 and WI, ignitron 1-2, contact FKI to bus LI. Current flowing from the terminal to the neutral builds up in winding W3 and the current in winding W2 decays.

Ignitron 1-4 is the next to conduct, and it conducts after 1-3 becomes non-conductive. Current then flows from bus L3 through ignitron 1-5, winding W3, winding W2, ignitron 1-4, contact FK2 to bus L2.

Finally, ignitron I-i conducts again after ignitron 1-2 becomes non-conductive and current flows from bus Li through contact FKI, ignitron I-I, windings WI and W2, ignitron 1-4, contact FKZ to bus L2.

A complete cycle of conduction of the ignitrons has now been completed. The ignitrons now continue to conduct in the above-described succession, and a reduced polyphase alternating voltage depending on the setting of the phase shift circuits PH is impressed on motor M.

Assuming that motor M is operating under load, its speed gradually increases and as it increases, the output of the tachometer generator G increases. Eventually suiiicient current is supplied to relay IRT to energize it so that it closes its contacts ITKZ through ITKfi in the firing circuits FCI through FC5. One of the resistors RP! in each firing circuit (FCI through FCG) is now shunted out and the phase of the firing potential is advanced. The output of the ignitrons I-I through 1-8 is now increased so that motor M is accelerated and its speed increases further. At a still higher speed of the motor, the relay 2RT is actuated closing all of its contacts ZTK! throu h 2TK5 and shunting out the other resistors RPZ in the firing circuits FCI through F06 of the ignitrons. The phase of the firing of the ignitrons is now further advanced and the ignitrons now operate in such manner as to supply substantially the full power to the motor. The motor is now operating at full speed and at the power factor corresponding to the full speed operation which. is determined by the setting of the variable resistor RP in the circuits PH.

It is to be noted that in certain situations in accordance with our invention, the fixed resistors which are shunted out by the relays ER! and ZRT are unnecessary as the voltage initially supplied to motor M is sufiiciently reduced for starting purposes by the setting of the variable resistor. As has been explained, this resistor is set to correspond to the running power-factor of motor M.

As motor M now rotates, the limit switches L-5 and L-S close. These switches shunt the presently closed contacts 6'! and 58 of the relay RR so that the operation is now independent of this relay, and the starting relay SR remains locked in through the contacts L4 and L-B independently of the relay RR. Next, the limit switches L-3 and L-4 close. A holding circuit for the relay RM is now closed through switch L-3 "14 which is independent of relay RR. This circuit extends from the auxiliary bus ALI through the conductor 91, the stop button BZ, contact S3, the

conductor 99, contact L-3, the now closed contact T5 of relay RM, the now closed contact 4| of relay RC, the conductor H3, the coil of relay RM, the now closed contact 8I of relay RM, the conductor I03, contact S4 to bus ALZ. Next contacts L-l and L-2 open. The opening of these contacts assures that relay RA2 which is locked in through them becomes deenergized and drops out. Relay RR which is energized through the contacts 53 and 65 of relay RAI also drops out and remains out regardless of the position of the run button BR. Motor M is thus prevented from going through more than one cycle of operation. Eventually, contacts L-5 and L-5 open and starting relay SR becomes deenergized and drops out. The supply of firing current to the ignitrons I-I through 1-6 is now interrupted and after the last two of the ignitrons to conduct has stopped conducting, the supply of power to motor M is stopped. A short time after switches L-5 and L-B open, switches 13-3 and L4 open and now relay RM is deenergized. The braking solenoid and the timer relay are now deenergized and motor M is stopped. Thereafter, the limit contacts L-I and L-2 reclose setting the system for a new operation.

If the operator releases the run button BR just after the contacts L-3 and L- I- close, but before the contacts L-I and L-2 open, relay RA2 remains energized through contacts L-I and L-2 and becomes deenergized when these contacts open. Once relay RA2 has been deenergized, the

S tandby-Continuous When the selector switch is set for continuous operation, contacts S3, S4, S5, S6, S1 and S8 are closed, and contacts SI and S2 are open. Under these circumstances, relays RC, RAI and RA2 of selector switch SS and contactor KF are energized as described with reference to the single cycle operation. In the case, however, the limit switch LS is ineffective because its contacts are shunted out at the contacts S5, S6, S1 and S8 of the selector switch SS.

Operatiow-Continuous To start continuous operation, the run button BR is pressed. Relay RAI is'then deenergized and drops out reopening its normally open contacts 5| and 53, but relay RA2 is not affected because it remains locked in through its now closed contacts 59 and 6|.

Relay RR is energized in a circuit extending from the bus ALI through the conductor 91, the stop button BZ, contact S3, the conductors 99 and IOI, the now closed contact 32 of the run button, the now reclosed contact of relay RAI the now closed contact 63 of relay RA2, the coil of relay RR, the now closed contact 65 of relay RA2, the now reclosed contact 51 of relay RAI, the conductor I03, contact S4 to bus ALZ.

As during the single cycle operation, relay the timer relay RT and the starting relay RS, are energized in sequence. Relay RM is now locked in through contact S5 in a circuit extending from the bus ALI through conductor 91, the stop button BZ, contact S3, contact S5, the now closed contact I5 of relay RM, the now closed contact 4| of relay RC, the coil of relay RM, another now closed contact 81. ofri'elay RM,-contact S4, to the bus ALZ.

When relay RS'is energized, the firing circuits FCI through FCfiior: the ignitrons 1-! through 1-6" are rendered efiective and the ignitrons conduct in the manner explained above. The conduction is initially at a relatively low voltage be- .cause the fixed resistors RP! and RP2 are connected in the phase-shifting circuits PH. As .the

speed of motor M increases, the relay IRT and lZRT are. actuated, increasing the voltage impressed on the motor until it is operating at full speed and at full voltage.

The release of run button BR does not aiiect the operation of motor M because the relay RM remains energizedindependently of the run button through its own now closed contacts and through the contacts of relay RC. The latter is energized independently of the run button BR through contacts S3 and S4.

1' The operation of the motor may be stopped by opening the stop button BZ through which both relay RMand R are locked in. Operation of this stop button causes relay RM to be deenergized and drop out, opening at its now open contacts Ti and '19 the circuits through the brake solenoid SB, the timer relay RT, and the starting relay RS.

' Standby-Inch When the selector switch SS is .set for inch operation, only contacts .Sl, S2, S1 and S8 are closed and the others are .open. Under these circumstances, relays RC, RA! and RAZ are deenergized and the operation is only through the relay RM or through the reversing relay RV, de-

pending on whether the inch forward BF or the inch reverse BV is closed.

-Operation-.Inch

To inch the motor forward, the inch forward button BF is actuated, opening its normally closed contact 3? to lock out the'inch reverse button BV and closing its normally open contact es. A circuit is now closed through relay RM which extends from bus ALI through the conductor 9?, the stop button BZ, contact SI, a conductor Ml, normally closed contactl43 of an auxiliary ,relay RAS, a conductor [45, the now closed contact as of the inch forward button Blithe normally closed contact 38 of the inch reverse button BV, the exciting coil of relay RM, the conductor H5, contact S2 to bus ALZ; Relay RM now closes but it is not locked in, since contacts S3 through S8 are open.

When relay RM is actuated, its lower contacts It? and [as close, closing the energizing circuit to the forward contactor KF, and conditioning the power supply unit to supply motor .M. In addition, the brake solenoid SBand the timer relay RT are energized in a circuit extending from the bus AL! through-now'closed .contact 11, the conductor I H, the excitingcoilof relayR'IZand the solenoid SB, the conductor H9, the now closed contact E9 of relay RM, the conductor l2! to the bus AL2. The timer relay RT picks up after it times out and through its upper now closed contact 83, it energizes the starting relay RS and the auxiliary relay RA3. Relay RS is energized in a circuit extending from bus ALI through the now closed contact 1'! of relay RM, the con ductor ll, contactuSL the conductors !23 and E25, the now closed contact 83 0f relay RT, the conductor I21, the exciting coil of relay RS, the conductor I29, the conductor 13!, the contact S8, the-conductor I33, nowoclcsed contact 19 of 15 relay RM,- the conductor 12! tobus ALE. The

circuit through the coil of relay RM is closed trons I-i through 1-6 and the latter conduct.

The normally closed contact Hit of relay RAS is opened, but relay RM remains locked in through the .nowsclosed contactof the timer relay RT and through the .inch forward button Motor M is now operated at reduced voltage and moves until the inch forward button is opened. When this button is opened, the relay RM and the relays, RT, RS and Rat and brake solenoid SB are deenergized and the movement of motor M is stopped. Motor M inched at a reduced voltage because the fixed resistors RP! and RP? remain connected in the circuit. If the inch forward button BF should be held closed an excessively long time, one or both of the relays iRT or 2RT would close, reducing the resistance in each phase shift circuit and increasing the power supply to the motor.

Repeated closing of the inch forward button BF repeats the above-described process and motorM is-inched forward as described.

To reverse the motor, the inch reverse button EV is actuated, opening the normally closed contact 38in circuit with the inch forward button BF and thus locking out the inch forward button and closing its normally opened contact 35. When the normally open contact closes, a circuit is completed through the coil of reversing relay RV which extends frozn'the bus ALi through the conductor 91,-thestop button BZ, the contact SI, the conductor Mi, the contact I43 of relay RAS, the conductor M5, the normally closed contact 37 of the inch forward button BF, the now closed contact 35 of the inch reverse button BV, the-coil of relay RV, a conductor iiil, contact S2 to bus AL2. Relay RV is now actuated and at its lower now closed contacts Si and 93 closes the energizing circuit for the reversing contactor KF. The reversing contacts RKE and RK2 are now closed and motor M is conditioned to operate in a reverse direction.

At its now closed contacts 8! and the reversing relay RV closes a circuit through the coil'of relay-RT and through the brake solenoid SB. This circuit extends from the bus ALi through the now closed contact 8? of the reversing relay RV, the conductors ill and 553, the coil of relay RT and the solenoid SB, the conductors H9 and 133, the now closed contact 89 of relay RV, the conductor 52!, to the bus ALE. The brake solenoid SB is energized and after a predetermined time interval, relay RT is actuated. This relay closes a circuit through the coil of starting relay RS which extends from the bus ALi through conductor 555, the now closed contact 8! of the reversing relay RV, contact St, the conductors E23 and 525, the now closed contact 83 of relay RT, the conductor 52?, the exciting coil of relay RS, the conductors its and I 3 5, contact SB, the conductor 533, the now closed contact 89 of reversing relay RV, the conductor 12! to bus ALZ. Relay RAE is energized in a similar circuit through the normally closed contact 49 of relay RC. The normally closed contact of relay RA3 opens, but the circuit through the exciting coil of relay RV remains closed through the now closed contact 35 of the timer relay RT.

When the starting relay RS is actuated, the firing circuits FCl through F08 for the ignitrons become eiTective and motor M is supplied at a reduced voltage. Since the reversing contacts RKI and RKZ are closed, the motor is operated in a reverse direction so long as the inch reverse switch remains closed. Once the inch reverse button EV is opened, the relay RV is deenergized and the operation. of motor M is stopped. Again if the inch reverse button BV remains closed for a substantial time interval, one or both of the relays IRT and ZR'I operate and the voltage impressed on motor M is increased.

Description Figure In the apparatus shown in Figs. 1A to 1D, the phase shift circuits PH for motor M is controlled by a tachometer generator, the output of which depends on the speed of the motor. This mode of control in accordance with our invention is particularly useful for a system in which motor M starts under load, and the increase in speed of motor M is dependent on the load. Since it is desirable that the relays I RT and ZRT operate as the motor reaches certain speeds, the tachometer generator G which responds to the speed is introduced for the purpose of acting the relays.

It frequently happens that a motor starts under no load and when it reaches full speed, is applied to the load. Such a motor is said to deliver a power stroke and encountered particularly in motors which drive directly a mechanical press particularly of the type used in forming automobile bodies.

A motor which rises to its full speed under zero load reaches certain of its speeds at predetermined time intervals after starting. In operating such a motor, the relays iRT and 2RT may be controlled from a timer rather than from a tachometer. A system of this type is shown in Fig. 5.

This system is similar to that disclosed in Figs. 1A to 113 including a polyphase motor M, an electronic power unit and a starting unit. The motor M, and the starting unit are so similar to those disclosed in Figs. 1A to 1D. The electronic power unit of Fig. 5 is also the same except that in place of the tachometer G, this unit includes a timer T from which the relays IRT and ZRT are actuated. This timer may be of the electronic or mechanical type, and may be of rather simple structure. The system also includes a starting relay RS5 which difiers from the starting relay RS of Figs. 1A through 1D in the fact that it includes in addition to the six contacts of the relay RS, an additional normally open contact SKT, which on closing energizes the timer T to start its timing operation.

Operation Figure 5 The operation of the Figure 5 system is similar to that of Figs. 1A to 1D. The selector switch of the starting circuit may be set for single cycle, continuous, or inch operation. Whatever the setting, once relay RM is actuated, relay RS5 is actuated. The latter relay not only closes the supply circuits for the firing capacitors C, but also energizes the timer T starting the timing operation.

The closing of the supply circuits for the firing capacitors renders the firing circuits for the ignitrons I-I through I-e' conductive and the latter conduct initially driving motor M at reduced voltage. At the same time, the timing operation starts. After a predetermined time interval, when motor M has reached a predetermined speed, relay IRT is actuated shunting out one fixed resistor RP! in each phase shift circuit PH. After another time interval when motor M has reached a still higher speed, relay 2RT is actuated shunting out the second resistor RP2 in each of the phase shift circuits. Motor M now reaches full speed and full voltage is applied in accordance with the setting of the variable resistor RP.

When the motor is to be deenergized, the relay RM in the starting circuit is deenergized and relay BS! is deenergized. The timer T is then reset and relays IRT and ZRT drop out.

Conclusion It is seen that we have provided a system in which a motor is started automatically at reduced voltage whether it is to be operated for single cycles, continuously or in inch. This system includes facilities for increasing the voltage applied to the motor as its speed increases.

The objects of our invention are accomplished in the embodiments disclosed by a pair of resistors RPI and RP2 which are shunted out in succession. Only two resistors are shown for illustrative purposes. Naturally a larger number of such resistors may be provided. The magnitudes of these resistors are not discussed in any detail. They may all be of the same magnitude or they may have substantially different magnitudes depending on the rate at which it is desirable to accelerate the motor.

Our invention is herein shown as including a Y connected motor M and the power circuit disclosed is similar to that shown in Fig. 1 of the above-mentioned parent application. Our invention in its broader aspects is applicable to motors connected in other ways, for example, as is shown in Figs. 2, 3 and 5 of the abovementioned parent application.

While we have shown certain specific embodiments of our invention, many modifications thereof are possible. Cur invention therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit thereof.

We claim as our invention:

1. In combination a polyphase motor having a plurality of phase windings each winding having a pair of terminals; a plurality of supply conductors corresponding in number to the phases of said motor and each adapted to be connected to a phase of a polyphase source; a pair of electric discharge paths each defined by an anode and a cathode and having a control electrode associated with each of said supply conductors; means for connecting anodes and cathodes of each of said pairs in antiparallel between its associated supply conductor and one terminal of an associated phase winding of said motor, means for interconnecting the remaining terminals of said windings; means c0n neoted between the control electrode and the cathode of each said path for rendering said path conductive at a predetermined instant in a half period of said source, said means being set to render each corresponding path conductive late in a half period of said source when power is first applied to said motor and means actuable as said motor gains speed to render each said path conductive substantially earlier in the half period of said source.

2. In combination an n phase motor having n phase windings each winding having a pair is of terminals; supply conductors adapted to beconneoted to the phases or an n phase source; it of electric discharge paths, each path being defined by an anode and a cathode and having a cont ol electrode and each pair being said supply conductors;

associated with one or means for connecting the anodes and cathodes of each of said pairs in anti-parallel between its associated. supply conductor and one te hinal of an associated. winding of said motor; means for interconnecting the remaining terminals of said windings, a circuit for controlling the conductivity of each of said paths connected between the control electrode the cathode of said path, each said circuit including mea s, normally effective to prevent its corresponding path from becoming conductive during any half period of said source until an instant late in said half period, and means for rendering said corresponding path conductive earlier in said half period when said preventing means is ine""ective; and means actuable as the speed of said motor increases for rendering said preventing means ineffective.

3, In combination an a phase motor having it phase windings each winding having a pair of terminals; a supply conductors adapted to be connected to the phases of an n phas source; 71, pairs of electric discharge paths, er ch path being defined by an anode and a cathode and having a control electrode and each pair being associated with one of said supply conductors; means for connecting the anodes and cathodes of each of said pairs in antiparallel between its associated supply conductor and one terminal of an associated winding of said motor; means for interconnecting the remaining terminals of said windings; a circuit for controlling the conductivity of each of said paths connected. between the control electrode and the cathode of said path, each said circuit including means normally effective to prevent its corresponding path from becoming conductive during any half period of said source until an instant late in said half period, and means for rendering said corresponding path conductive substantially earlier in said half period when said preventing means is ineffective; and means responsive to the speed of said motor for rendering said preventing means ineffective.

i, In combination an n phase motor having at phase windings each winding having a pair of terminals; or supply conductors adapted to be connected to the phases of an n phase source; n pairs of electric discharge paths, each path being defined by an anode and a cathode and having a control electrode and each pair being associated with one of said supply conductors; means for connecting the anodes and cathodes of each of said pairs in anti-parallel between its associated supply conductor and. one terminal of an asso-' ciated winding of said motor; means for interconnecting the remainin terminals of said windings, a circuit'for controlling the conductivity of ea ch of said paths connected between the control electrode and the cathode of said path, each said circuit including means normally effective to prevent its corresponding path from becoming conductive during any half period of said source until an instant late in said half period, and means for rendering said corresponding path conductive substantially earlier in said half period when said preventing means is ineffective; and timing means actir: ble a predetermined time interval after the motor has been energized for rendering said preventing means incfiective.

substantially '5. In combination an n phase motor having 1!, phase windings each winding having a pair of terminals; n supply conductors adapted to be connected to the phases of an 11, phase source; 11 pairs of electric discharge paths, each path being defined by an anode and a cathode and having a control electrode and each pair being associated with one of said supply conductors; means for connecting the anodes and cathodes of each of said pairs in anti-parallel between its associated supply conductor and one terminal of an associated winding of said motor; means for interconnecting the remaining terminals of said windings, a circuit for controlling the conductivity of each of said paths connected between the control electrode and the cathode of said path, each said circuit including means normally effective to pre= vent its corresponding path from becoming con= ductive during any half period of said source until an instant late in said half period, and means for rendering said corresponding path conductive substantially earlier in said half period when said preventing means is ineiiective; 'said preventing means having a plurality of settings for setting said instant over a predetermined range during said half period, and timin means actuable at successive time intervals after the motor has been energized to change the settings of said preventing means to render each said path conductive progressively earlier during the half periods of said source.

6, In combination an n phase motor having '11, phase windings each winding having a pair of terminals; 17, supply conductors adapted to be connected to the phases of an a phase source; 12 pairs of electric discharge paths, each path being defined by an anode and a cathode and having a control electrode and each pair being associated with one of said supply conductors; means for connecting the anodes and the oathodes of each of said pairs in antiparallel between the associated supply conductor and one terminal or an associated phase winding; means for interconnecting the remaining terminals of said windings; a circuit for controlling the conductivity of each of said paths connected between the control electrode and the cathode of said path, said circuit including means having a plurality of settings in each of which said path is prevented from being rendered conductive until a predetermined instant diiierent for each setting, in any half period of said source, said circuits being set for all said paths, when said motor is initially energized, in a setting in which paths are prevented from becoming conductive until late in the half periods of said source; and means ac tuable as the speed of said motor increases for resetting said preventing means to permit said paths to be rendered conductive earlier in said half periods.

'7. In combination an n phase motor having n phase windings each winding having a pair of terminals; a supply conductors adapted to be connected to the phases of an 11 phase source; n pairsof electric discharge paths, each path being defined by an anode and a cathode and having a control electrode and each pair being associated with onset said supply conductors; means for connecting'thc anodes and the cathodes of each of said pairs in antiparallel between the associated supply conductor and one terminal of an associated phase winding; means for interconnecting the remaining terminals of said windings; a circuit for controlling the conductivity of each of said paths connected between the ontrol electrode and the cathode of said path, circuit including means having a plurality i settings in each of which said path is prevented from being rendered conductive until a redetermined instant, different for each setting, n any half period of said source, said circuits eing set for all said paths, when said motor is initially energized, in a setting in which said paths are prevented from becoming conductive until late in the half periods of said source; and means responsive to the speed of said motor and actuable as the speed of said motor increases for progressively resetting said preventing means to permit said paths to be rendered conductive progressively earlier in said half periods.

8. In combination an n phase motor having 12 phase windings each winding having a pair of terminals; a supply conductors adapted to be connected to the phases of an n phase source; n pairs of electric discharge paths, each path being defined by an anode and a cathode and having a control electrode and each pair being associated with one of said supply conductors; means for connecting the anodes and the oathodes of each of said pairs in antiparallel between the associated supply conductor and one tor-- minal of an associated phase winding; means for interconnecting the remaining terminals of said windings; a circuit for controlling the conductivity of each of said paths connected between the control electrode and the cathode of said path, said circuit including means having a plurality of settings in each of which said path is prevented from being rendered conductive until a predetermined instant, different for each setting, in any half period of said source, said circuits being set for all said paths, when said motor is initially energized, in a setting in which said paths are prevented from becoming conductive until late in the half periods of said source; means actuable as the speed of said motor increases for resetting said preventing means to permit said paths to be rendered conductive earlier in said half periods, and selective means connected to said circuits for actuating said circuits to drive said motor continuously or to inch said motor.

9. Apparatus according to claim 6 characterized by the fact that each circuit includes one setting in which the paths are prevented from becoming conductive until an instant in any half period or the source which is substantially later than the instant in said halr" period corresponding to the lowest power-factor at which the motor operates.

10. In combination an n phase motor having 11. phase windings, each winding having a pair of terminals; n supply conductors adapted to be connected to the phases or an 1?. phase source; 11 pairs or electric discharge paths, each path being donned by an anode and a cathode and having a control electrode and each pair or being associated with one or said supply conductors; means lor connecting the anodes and cathodes oi each or said pairs in antlparallel between its associated supply conductor and one terminal or an associated Winding of said motor; means for interconnecting the remaining terminals 01 said wlndlngs; and a circuit ior controlling the conductivity 01 each of said paths connected between the control electrode and the cathode of said path, each said circuit including means for preventing said path Irom becoming conductive during any half period of said source on: CD

a at

until an instant corresponding to the normal running power-factor of said motor.

11. In combination an n phase motor having it phase windings, each winding having a pair of terminals; n supply conductors adapted to be connected to the phases of an 11. phase source; 71. pairs of electric discharge paths, each path being defined by an anode and a cathode and having a control electrode and each pair being associated with one of said supply conductors; means for connecting the anodes and cathodes of each of said pairs in antiparallel between its associated supply conductor and one terminal of an associated winding of said motor; means for intercom necting the remaining terminals of said windings, a circuit for controlling the conductivity of each of said paths connected between the control electrode and the cathode of said path, each said circuit including means for preventing said path from becoming conductive during any half period of said source until an instant corresponding to the normal running poweractor of said motor;

and selective starting means connected to said circuits for actuating said circuits to operate said motor continuously or to inch said motor.

12. In combination a heavy-duty motor; a power unit for said motor including controllable electric discharge devices and means to be actuated for rendering said discharge devices conductive, said rendering means being so set in its quiescent state that said discharge devices are initially adapted to operate at reduced conductivity; means adapted to interpose said power unit electrically between said motor and a power source so that said motor is supplied from said source through said discharge devices; and a starting unit for said motor connected to said power unit for actuating said rendering means, said starting unit including means for actuating said rendering means to operate said motor at the will of an operator for at least one cycle of operation or in inch; said power unit including means actuable as the speed or" said motor increases for increasing the conductivity of said devices.

13. The combination according to claim 12 characterized by the fact that the actuable means includes a timer and by means included in the starting unit for starting the timing of said timer simultaneously with the actuating of said rendering means.

14. In combination a heavy-duty motor; a power unit for said motor including controllable electric discharge devices and means to be actuated for rendering said discharge devices conductive, said rendering means being so set in its quiescent state that said discharge devices are initially adapted to operate at reduced conductivity; means adapted to interpose said power supply unit electrically between said motor and a power source so that said motor is supplied from said source through said discharge devices; and a starting unit for said motor connected to said power unit for actuating said rendering means, said starting unit including means for actuating said rendering means to operate said motor at the will of an operator for at least one cycle of operation or in inch; said power unit including means responsive to the speed of said motor and actuable as the speed of said motor increases for increasing the conductivity of said devices.

WILLIAM E. LARGE. ROBERT F. BARRELL.

No reference cited. 

